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Mannanase hydrolysis of spruce galactoglucomannan focusing on the influence of acetylation on enzymatic mannan degradation
Chalmers Univ Technol, Div Ind Biotechnol, Dept Biol & Biol Engn, S-41296 Gothenburg, Sweden.;Chalmers Univ Technol, Wallenberg Wood Sci Ctr, S-41296 Gothenburg, Sweden..
KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Glycoscience.
KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Centres, Wallenberg Wood Science Center.
Chalmers Univ Technol, Div Ind Biotechnol, Dept Biol & Biol Engn, S-41296 Gothenburg, Sweden.;Chalmers Univ Technol, Wallenberg Wood Sci Ctr, S-41296 Gothenburg, Sweden..
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2018 (English)In: Biotechnology for Biofuels, ISSN 1754-6834, E-ISSN 1754-6834, Vol. 11, article id 114Article in journal (Refereed) Published
Abstract [en]

Background: Galactoglucomannan (GGM) is the most abundant hemicellulose in softwood, and consists of a backbone of mannose and glucose units, decorated with galactose and acetyl moieties. GGM can be hydrolyzed into fermentable sugars, or used as a polymer in films, gels, and food additives. Endo-beta-mannanases, which can be found in the glycoside hydrolase families 5 and 26, specifically cleave the mannan backbone of GGM into shorter oligosaccharides. Information on the activity and specificity of different mannanases on complex and acetylated substrates is still lacking. The aim of this work was to evaluate and compare the modes of action of two mannanases from Cellvibrio japonicus (CjMan5A and CjMan26A) on a variety of mannan substrates, naturally and chemically acetylated to varying degrees, including naturally acetylated spruce GGM. Both enzymes were evaluated in terms of cleavage patterns and their ability to accommodate acetyl substitutions. Results: CjMan5A and CjMan26A demonstrated different substrate preferences on mannan substrates with distinct backbone and decoration structures. CjMan5A action resulted in higher amounts of mannotriose and mannotetraose than that of CjMan26A, which mainly generated mannose and mannobiose as end products. Mass spectrometric analysis of products from the enzymatic hydrolysis of spruce GGM revealed that an acetylated hexotriose was the shortest acetylated oligosaccharide produced by CjMan5A, whereas CjMan26A generated acetylated hexobiose as well as diacetylated oligosaccharides. A low degree of native acetylation did not significantly inhibit the enzymatic action. However, a high degree of chemical acetylation resulted in decreased hydrolyzability of mannan substrates, where reduced substrate solubility seemed to reduce enzyme activity. Conclusions: Our findings demonstrate that the two mannanases from C. japonicus have different cleavage patterns on linear and decorated mannan polysaccharides, including the abundant and industrially important resource spruce GGM. CjMan26A released higher amounts of fermentable sugars suitable for biofuel production, while CjMan5A, producing higher amounts of oligosaccharides, could be a good candidate for the production of oligomeric platform chemicals and food additives. Furthermore, chemical acetylation of mannan polymers was found to be a potential strategy for limiting the biodegradation of mannan-containing materials.

Place, publisher, year, edition, pages
BIOMED CENTRAL LTD , 2018. Vol. 11, article id 114
Keywords [en]
Lignocellulose, Spruce, Galactoglucomannan, Endo-beta-mannanases, GH5, GH26, Cellvibrio japonicus, Polysaccharide acetylation, Enzymatic degradation pattern, Acetyl esterases
National Category
Chemical Sciences
Identifiers
URN: urn:nbn:se:kth:diva-227774DOI: 10.1186/s13068-018-1115-yISI: 000430977200001PubMedID: 29713374Scopus ID: 2-s2.0-85045688074OAI: oai:DiVA.org:kth-227774DiVA, id: diva2:1205443
Funder
Knut and Alice Wallenberg FoundationSwedish Research Council, 621-2014-5295
Note

QC 20180514

Available from: 2018-05-14 Created: 2018-05-14 Last updated: 2019-01-07Bibliographically approved
In thesis
1. Wood Hemicelluloses - Fundamental Insights on Biological and Technical Properties
Open this publication in new window or tab >>Wood Hemicelluloses - Fundamental Insights on Biological and Technical Properties
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Hemicelluloses are a group of heterogeneous polysaccharides representing around 30 % of wood where the dominating types are xylans, glucomannans and xyloglucans. Hemicelluloses complex molecular structure makes it difficult to understand the relationship between structure and properties entirely, and their biological role is not yet fully verified. Additionally, hemicelluloses are sensitive to chemical processing and are not utilized to their full potentials for production of value-added products such as materials, additives to food and pharmaceutical products, etc. Increased knowledge regarding their functions is important for the development of both processes and products. The aim with this work has therefore been to increase the fundamental understanding about how the structure and properties of wood hemicelluloses are correlated, and properties such as flexibility, interaction with cellulose, solubility, resistance to chemical-, thermal-, and enzymatic degradation have been explored.

Molecular dynamics (MD) simulations were used to, in detail, study the structures found in wood hemicelluloses. The flexibility was evaluated by comparing the impact of backbone sugars on the conformational space and also the impact of side groups was considered. Based on the conformational space of backbone glycosidic linkages the flexibility order of hemicelluloses in an aqueous environment was determined to be: xylan > glucomannan > xyloglucan. Additionally, the impact of xylan structure on cellulose interaction was evaluated by MD methods.

Hemicelluloses were extracted from birch and spruce, and were used to fabricate different composite hydrogels with bacterial cellulose. These materials were studied with regards to mechanical properties, and it was shown that galactoglucomannans mainly contributed to an increased modulus in compression, whereas the most significant effect from xylan was increased strain under uniaxial tensile testing. Besides, other polysaccharides of similar structure as galactoglucomannans were modified and used as pure, well defined, models. Acetyl groups are naturally occurring decorations of wood hemicelluloses and can also be chemically introduced. Here, mannans with different degrees of acetylation were prepared and the influence of structure on solubility in water and the organic solvent DMSO were evaluated. Furthermore, the structure and water solubility influenced the interaction with cellulose. Acetylation also showed to increase the thermal and biological stability of mannans.

With chemical pulping processes in mind, the degradability of spruce galactoglucomannans in alkaline solution were studied with regards to the structure, and the content of more or less stable structural regions were proposed.

Abstract [sv]

Hemicellulosor är en grupp av heterogena polysackarider som utgör ca 30 % av trä och där de vanligaste typerna är xylaner, glukomannaner och xyloglukaner. Den komplexa strukturen gör det svårt att fullständigt förstå förhållandet mellan struktur och egenskaper, och deras biologiska roll är ännu inte fullständigt kartlagd. Dessutom är hemicellulosor känsliga för kemiska processer och tas inte tillvara på bästa sätt för att tillverka förädlade produkter så som nya material eller användas som additiv till livsmedel och farmaceutiska produkter etc. En ökad kunskap om deras funktion är viktig för utvecklingen av både processer och material. Målet med detta arbete har därför varit att öka den fundamentala förståelsen för hur struktur och egenskaper hos hemicellulosor från trä hänger ihop. Egenskaper så som flexibilitet, interaktion med cellulosa, löslighet, samt kemisk-, termisk- och biologisk stabilitet har utvärderats.

Molekyldynamiska (MD) simuleringar användes för att studera strukturer som återfinns i hemicellulosor på detaljnivå. Flexibiliteten utvärderades med avseende på hur konformationsrymden påverkades av vilka monosackarider som ingick i huvudkedjan, samt påverkan från sidogrupper. Baserat på huvudkedjan bör flexibilitetsordningen för studerade hemicellulosor i vattenlösning vara: xylan > glukomannan > xyloglukan. Dessutom användes MD simuleringar för att analysera hur strukturen hos xylaner påverkar interaktionen med cellulosa.

Hemicellulosor extraherades från björk och gran, och användes för att producera flera olika komposithydrogeler med bakteriell cellulosa. Dessa material studerades bland annat med avseende på de mekaniska egenskaperna och de tydligaste observationerna var att galaktoglukomannan bidrog till en ökad kompressionsmodul, medan xylan framförallt ökade töjbarheten i dragprov. Dessutom modifierades modellpolysackarider med liknande struktur som galaktoglukomannan och användes som extra rena och väldefinierade modellsystem. Acetylgrupper förekommer naturligt som sidogrupper på hemicellulosor och de kan även introduceras via kemisk modifiering. I detta projekt tillverkades mannaner med olika acetyleringsgrad och hur strukturen påverkade lösligheten i vatten och det organiska lösningsmedlet DMSO utvärderades. Det visade sig även att strukturen och lösligheten i vatten påverkade interaktionen med cellulosa. Acetyleringen hade också en positiv effekt på den biologiska och termiska stabiliteten.

Med kemiska massaprocesser i åtanke studerades nedbrytbarheten hos galaktoglukomannaner från gran i alkalisk lösning med avseende på strukturen och förekomsten av mer eller mindre stabila strukturella regioner föreslogs.

Place, publisher, year, edition, pages
Stockholm, Sweden: KTH Royal Institute of Technology, 2018. p. 82
Series
TRITA-CBH-FOU ; 2018:63
Keywords
hemicellulose, wood, glucomannan, xylan, structure, acetylation, flexibility, solubility, interaction with cellulose, stability., hemicellulosa, trä, glukomannan, xylan, struktur, acetylering, flexibilitet, löslighet, interaktion med cellulosa, stabilitet.
National Category
Wood Science Chemical Sciences Paper, Pulp and Fiber Technology Plant Biotechnology
Research subject
Fibre and Polymer Science
Identifiers
urn:nbn:se:kth:diva-240982 (URN)978-91-7873-068-1 (ISBN)
Public defence
2019-02-01, F3, Lindstedtsvägen 26, Stockholm, 10:00 (English)
Opponent
Supervisors
Funder
Knut and Alice Wallenberg Foundation
Note

QC 20190107

Available from: 2019-01-07 Created: 2019-01-07 Last updated: 2019-01-07Bibliographically approved

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